This invention relates to methods of treating a subterranean formation, and in particular to treatment methods with a high density brine and xanthan gum.
Xanthan gum is often used to viscosify brines to prepare gravel packing fluids. References disclosing xanthan fluids for gravel packing include, for example, U.S. Pat. No. 6,976,538, U.S. Pat. No. 6,987,083, U.S. Pat. No. 7,090,015, U.S. Pat. No. 7,216,704 and WO 98/06972. However, applicant has found that xanthan-viscosified cesium formate brines can form solid or solid-like hydrogels over a period of time. As used herein, the terms “hydrogel,” “viscous hydrogel,” and “solid hydrogel” refer interchangeably to solid or solid-like xanthan-containing brines, as distinguished from the term “gel” which refers to xanthan-viscosified brines that have a viscosity on the order of tens, hundreds or perhaps thousands of mPa-s so that they readily flow and can be easily pumped through a pipe or tubing. The formation of such high viscosity hydrogels is detrimental to the use of these fluids for well treatment operations such as gravel packing, due to the anticipated difficulty of pumping these materials. There exists a need for a method to prepare xanthan-viscosified brines comprising cesium formate.